An introduction to Gymnasium Acoustics

Over the years, I’ve received a lot of calls from Gymnasium owners in India wanting to improve the sound within their spaces. Generally gyms have lots of hard reflective surfaces and a resulting lack of speech intelligibility. The first thought for sound control is usually acoustical wall panels, and these absorb sound but also water and therefore, have one strike against them because people sweat in gyms and this creates a lot of humidity. In this case, absorptive ceiling panels for low ceilings and hanging acoustical baffles for high ceilings are usually the best choice for sound absorption without moisture absorption. They are also the best place to begin treatment for a gymnasium.

Initially, it seems counter intuitive not to treat the wall first, after all, isn’t the sound bouncing off the walls and around the room? True, but the typical gym may have a reverberation time of between three to seven seconds. While an echo is a discrete reflection, reverberation is a series of non-directional, indistinguishable reflections. The sound appears to be everywhere. The best means of reducing long reverberation times is to add the most exposed, acoustically absorptive material into the space. Hanging baffles, with two sides exposed to the sound as well as edges, have that.

Using Nankarrow NeoSquare™ panels works best for gymnasiums with a ceiling height of under 12 feet. Usually, covering 100% of the slab ceiling will give you absorption approaching the theoretical limit of 1.0, but covering even 50% of the ceiling will give excellent results, especially if the ceiling has non-reflective panels.

A 2’ X 4’ hanging baffle made from Nankarrow NeoMax™ panels has twice the surface area of a wall panel of the same size plus the edge area which may not be exposed if wall panels are mounted contiguously. A 4-inch thick baffle (made by sticking two Nankarrow NeoMax™ panels on either side of hardboard) has 18 square feet of absorptive area with a coefficient approaching the theoretical limit of 1.00. A wall panel would be limited to its front surface of eight square feet with the same coefficient.

The next stage is to control side-to-side reflections by adding wall panels where a direct reflection produces an annoying echo. Since reverberation is being brought down by the hanging baffles, and there is gym equipment and wall racks to break-up the reflections (scattering and diffusion), fewer are needed. However, it is recommended that they be high-impact to avoid damage from a direct hit by basketballs, if the gym is active. The ceiling baffles will dodge and “duck” out of the way, if an object travels high enough to reach them.

To paraphrase a line from a classic movie song: “A gym is still a gym.” It should sound still like one, just better. Compromise of the ideal reverb time for each intended function will allow the broadest use of the facility. A modern sound engineer (and for that matter the speaker) may prefer a very dry room for intelligibility with electronics used to add-back ambience when needed. An overly “dead” sounding gym will create a sonic disconnect with the visual space, somewhat disorienting, like a studio recording “dubbed-in” to a live, outdoor sound track, without matching ambience to surroundings.

In summary, Nankarrow NeoMax™ and Nankarrow NeoSquare™ are the lowest cost, most efficient and least intrusive means to tame gymnasium reverb, no matter how large or small.